GB2541917A

GB2541917A - A method for welding wires comprising aluminium

Info

Publication number: GB2541917A
Application number: GB1515669.8A
Authority: GB
Inventors: James Allen Timothy; Edward Allen Mark
Original assignee: Tirius Ltd
Current assignee: Tirius Ltd
Priority date: 2015-09-04
Filing date: 2015-09-04
Publication date: 2017-03-08
Also published as: GB201515669D0

Abstract

A method suitable for welding aluminium wires comprising, placing a plurality of aluminium wires 1 proximal a connector 2, heating said wires and said connector forming at least one weld pool and allowing said weld pool to solidify such that the wires are welded to the connector. Further method steps may be included comprising inserting said wires through a first aperture 2a into said connector and protruding from a second aperture 2b in said connector, heating an aluminium filler material providing additional material to the weld pool, undertaking the welding at an aperture in the connector, insulating the wires 3, welding the wires joined to the connector to at least one further plurality of aluminium wires joined to at least one further connector, welding the wires joined to the connector to at least one further component and striking an arc between 60 and 100 Amps with an arc maintenance current of between 20 and 60 Amps during tungsten inert gas welding. The connector may comprise aluminium and its aperture be closed by the solidified weld pool. The connector and wires may have the same/different elemental compositions and the welding process result in localised heating of said wires and said connector.

Description

A Method for Welding Wires Comprising Aluminium Field of the invention

The present invention relates a method of joining aluminium; in particular a method of welding electrical winding wires.

Background to the invention

The use of aluminium wires to carry electrical current is a developing technology. The use of aluminium wires as an alternative to the previously ubiquitous copper wires has benefits, such as a reduction in the cost of the raw materials to form these connections and the weight associated with them. These benefits are of considerable advantage in many modern day technologies where a large number of electrical connections are required, for example, but not limited to, hybrid vehicle engines which utilise both fossil fuels and electric power.

However, the replacement copper wiring in these areas of technology with wires based on aluminium alloys raises several new technical issues, such as the requirement for reliably joining lengths of aluminium wire. Whilst methods of joining copper wires to one another, such as brazing, soldering and crimping, are numerous and well understood, these methods are not suitable for the joining of aluminium wires.

It is common to join aluminium wires to one another via crimping and the use of crimped connections. Here, the aluminium wires to be joined may be placed into a crimp, most commonly a hollow cylinder or similar, and this crimp then deformed to hold the wires to be connected in place with a mechanical force. The use of crimped connections with aluminium wires is, however, unsatisfactory in many regards.

Due to the relative softness of the aluminium wires, compared to that of the copper wires, the crimps required for aluminium wires are larger than those used in the case of copper wires. This increase in size of the crimps is necessitated to ensure a sufficient compressive force is applied to the joint to secure the wires in place. Additionally, the deformation of the aluminium crimp during the joining process results in its expansion along the length of the wires, further increasing the bulk of the connector. Whilst these increases in the size of the crimped connection, compared to those required in the case of copper wires, may be tolerable in some circumstances, in applications where the joints must be tightly packaged, or space is at a premium, this drawback may be unacceptable.

It is also the case that such crimped joints have disadvantages when it comes to the long term durability of the joint. Crimped joints are open and are therefore subject to corrosion. Whilst the issue of corrosion may be mitigated with the use of a corrosion inhibiting grease in the joint, such a grease may increase the electrical resistivity of any connection, a clear disadvantage to its use. Furthermore, said corrosion inhibiting grease may be washed or rubbed away and, as such, does not represent a long term ‘set and forget’ solution to the corrosion of the crimped joints.

Composite crimps made from aluminium and copper can be used to avoid some of the corrosion issues associated with thermal and electrical cycling of the crimped joint, although these crimps remain bulky and introduce problems associated with differences in thermal expansion coefficient. Alternatively, the use of encapsulants has also been trialled to reduce oxidation, although these see an increase in the complexity of the joint without a concomitant increase in its overall performance.

When considering the joining of aluminium wires, an alternative to crimping is the use of cold formed copper and aluminium joints for individual wires. In this case, every individual wire must be joined to another separately in cold forming process using a pressure die. Whilst this method of joining produces a consistent joint between the two wires, it is a long and laborious process; in any application employing multi strand wiring each joint must be individually mechanically supported and insulated. Once again, there are also issues surrounding the use of dissimilar materials in the joint leading to problems with thermal expansion, and the subsequent need for a second copper to aluminium joint to effect an overall aluminium to aluminium joint further increasing the complexity of such a solution.

Traditionally, the joining of aluminium wires may also be undertaken with brazing or electrical welding techniques, such techniques require the use of an inert shrouding gas or flux. With this method of joining, the production of a large cohesive joint requires the introduction of significant heat energy, often causing damage to the insulation layer of the aluminium wires, or other parts associated with the joint. Additionally, a filler material with different electric or thermal properties to the bulk aluminium wire may also be required. As such, the use of braising or electrical welding techniques to join aluminium wires has numerous disadvantages.

Embodiments of this invention seek to address these problems.

Summary of the invention

According to a first aspect of the present invention, there is provided a method for welding wires comprising aluminium, the method comprising the steps of, placing a plurality of wires comprising aluminium proximal to a connector, heating said plurality of wires comprising aluminium and said connector to form at least one weld pool, and allowing said weld pool to cool and form a solidified weld pool such that said plurality of wires is welded to said connector.

In this way, a method of welding wires comprising aluminium suitable for carrying an electrical current is provided. Such a method is advantageous as it results in a connection of reduced size compared to existing technologies, advantageous where a connection is required in tightly packaged technologies, for example hybrid power units. Additionally, such a method for welding wires comprising aluminium is advantageous as there may be no degradation of the joint over time due to corrosion, due to the presence of a protective aluminium oxide layer on its external surfaces.

Preferably, the method may further comprise the step of inserting said plurality of wires into said connector. Such an embodiment of the invention may be preferable as it may improve the strength of the welded connection between the plurality of wires comprising aluminium and the connector.

It may also be preferable for the method to further comprise the step of inserting said plurality of wires into said connector, such that said plurality of wires pass through a first aperture in said connector and protrude from a second aperture in said connector. In this case, the strength of the connection between the plurality of wires and the connector may be further increased. Additionally, in such an embodiment, it may be possible to form a plurality of welds between each of the plurality of wires comprising aluminium and the connector.

Preferably, said connector may also comprise aluminium. Such an embodiment of this invention may be advantageous as, in this case, the finished joint and solidified weld pool will also comprise aluminium. In this case, the degradation of the joint over its lifespan may also be reduced, as any issues resulting from the differing mechanical properties of the materials used in the joint will become less prevalent. For example, any problems resulting from differences in the coefficient of thermal expansion of the joint material may be less severe or even eliminated.

It may also be preferable for the method to further comprise a step wherein a filler material is heated to provide additional material to said weld pool as part of the welding process. An embodiment of this form may be advantageous as it may ensure there is sufficient material in the weld pool to allow the wires comprising aluminium to be effectively bonded to the connector. Additionally, it may be possible to alter the composition of the filler material to achieve the desired mechanical and, or electrical properties of the joint.

Preferably, the filler material may comprise aluminium. Once again, such an embodiment may be preferable as any issues resulting from differences in the physical properties of the materials used in the join may be reduced. Additionally, the use of an aluminium filler material may help ensure the join is protected from corrosion with a layer of aluminium oxide.

In some embodiments of this invention, it is preferable for the welding process to be undertaken at an aperture in the connector. Such an embodiment may be preferable as, in this case, each of the wires comprising aluminium may be exposed to heat in the welding process. Therefore, in such an embodiment, each of the wires may be joined effectively to both each other and the connector. As such, a joint with good electrical and mechanical properties at both the multiple and single wire levels may be formed.

Additionally, it may be preferable for the method to comprise a step wherein at the termination of the welding process, said aperture in the connector is closed by said solidified weld pool. Such an embodiment may be preferable as the aperture in the connector being closed by the solidified weld pool may further ensure an acceptable electrical and physical connection between each of the wires and the connector. Above this, the provision of an aperture which has been closed off by the weld pool may be preferable as it may provide a relatively flat, smooth surface upon which any further joining processes may be undertaken.

Preferably, the method of welding may further comprise a step of insulating the plurality of wires comprising aluminium. Such an embodiment may be preferable as electrical current may be unable to pass between individual wires in the plurality of wires comprising aluminium in areas other than the join. Such a method of carrying electricity has many advantages including a reduction in the skin effect, concerning the electrical resistance of a wire at high frequencies of alternating current, and a reduction in the proximity effect, where energy losses are caused by electromagnetic forces.

In some embodiments, it may be preferable for the connector and the plurality of wires comprising aluminium heated to form said weld pool to have the same elemental composition as one another. In such an embodiment, the use of the same elemental composition in both the connector and the plurality of wires comprising aluminium may cause the join to have electrical and mechanical properties similar to those of the bulk wire.

Alternatively, it may be preferable for the connector and the plurality of wires comprising aluminium heated to form said weld pool to have differing elemental compositions. In such an embodiment, it may be possible to tailor the composition of molten weld pool, and thus the solidified weld pool, to achieve the desired electrical and mechanical properties of the joint. In differing embodiments, these electrical and mechanical properties may be different to, or the same as, the mechanical and electrical properties of the bulk wire.

Preferably, the welding process may only result in localised heating of the plurality of wires comprising aluminium and the connector. Such an embodiment may be preferable as any coating on the wire, such as an insulating coating, may remain undamaged proximal to the joint after the welding process. Additionally, a reduction in the heating of the materials of the joint may reduce or prevent any changes in the metallurgy of the joint during the welding process, preserving the mechanical and electrical properties of the completed joint in relation to the pre-joined materials.

In another embodiment of the invention, it may be preferable for the method to further comprise the step of welding the plurality of wires comprising aluminium joined to the connector to at least one further plurality of wires comprising aluminium joined to at least one further connector. In such an embodiment, two pluralities of wires comprising aluminium may be reliably joined together effectively in a space efficient manner.

Preferably, the method may also contain a further step of welding the plurality of wires comprising aluminium joined to the connector to at least one further component. Here, the plurality of wires comprising aluminium may be reliably and rapidly joined to another component as required, whilst preserving the advantages of the original joint.

It may also be preferable for the method to further comprise the step of using tungsten inert gas welding. It may be advantageous to use such a welding process as it is well understood, and the equipment required to undertake such a process is commonly available.

Preferably, the method may further comprise the step of striking an arc between 100 and 60 Amps, more preferably between 90 and 70 Amps and most preferably at 80 Amps during the tungsten inert gas welding process. The use of such a current is preferable as it is relatively low and thus may reduce the cost of the welding process. Additionally, the use of a low current may reduce the temperature increase seen in areas proximal to the joint during the welding process.

Preferably, the method may further comprise the step of using a current of between 20 and 60 Amps, more preferably between 30 and 50 Amps and most preferably .40 Amps during the tungsten inert gas welding process. Once again, the use of a current in this range is relatively low, potentially reducing the cost of the welding process and reducing the temperature increase seen in areas proximal to the joint during the welding process.

Preferably, the method for welding wires comprising aluminium may take a form substantially as hereinbefore described with reference to the accompanying drawings.

According to a second aspect of the present invention, there is provided a connection between a plurality of wires comprising aluminium and a connector, the connection obtained by the method of any one preceding claim.

Detailed Description

The invention will now be described by way of example with reference to the following figures in which:

Figure 1 schematically illustrates a plurality of wires and a connector;

Figure 2 schematically illustrates the plurality of wires inserted into the connector;

Figure 3 schematically illustrates the welding of the plurality of wires to the connector;

Figure 4 schematically illustrates the plurality of wires welded to the connector;

Figure 5 schematically illustrates two connectors welded to each other.

Referring first to figure 1, here a plurality of wires comprising aluminium 1 is shown along with a connector 2. In this embodiment of the invention, each of the wires comprising aluminium 1 is coated in a layer of insulating material 3 and the connector 2 is a cylindrical tube of an aluminium alloy.

With respect to figure 2, the plurality of wires comprising aluminium 1 is shown inserted into the connector 2 through a first aperture 2a in such a way that the plurality of wires comprising aluminium 1 may be constrained by the connector 2 and be seen though a second aperture 2b.

Figure 3 depicts the welding of the plurality of wires comprising aluminium 1 such that they are joined with the connector 2. In this embodiment of the invention, tungsten inert gas welding is used to join the plurality of wires comprising aluminium 1 to the connector 2. In this technique, the area to be welded is protected by an inert shielding gas (typically argon or helium) whilst an electrical arc is generated between a non-consumable tungsten electrode and both the plurality of wires comprising aluminium 1 and the connector 2. In this embodiment, the electrical arc may be generated at a current of 80- Amps and sustained during the welding process at a current of 40 Amps.

During the tungsten inert gas welding process, areas of both the plurality of wires comprising aluminium 1 and the connector 2 are heated by the welding arc and may become molten, forming a weld pool comprising molten aluminium. Upon removal of the welding arc from the proximity of the weld pool, the weld pool may begin to cool and solidify, forming a join between the plurality of wires comprising aluminium 1 and the connector 2. In this embodiment, the solidification of the weld pool closes the second aperture in the connector 2.

Additionally, a filler material 4 may be used to supply additional material to the weld pool. In this embodiment of the invention, the filler material 4 comprises aluminium. The addition of filler material 4, also melted by the heating action of the welding arc, to the weld pool may ensure there is sufficient molten material in the weld pool to ensure a resilient join between the plurality of wires comprising aluminium 1 and the connector 2.

During the welding process, both the plurality of wires comprising aluminium 1 and the connector 2 only increase in temperature in an area proximal to the welding arc, due to the localised nature of the welding process. In this case, the insulating material and other materials surrounding the joint may remain unaffected by an increase in temperature due to the welding process.

Figure 4 depicts a solidified join between the plurality of aluminium comprising wires 1 and a connector 2. The solidified weld pool 5 is depicted, where the plurality of aluminium containing wires 1 is joined to the connector 2.

Figure 5 depicts a further embodiment of the invention where two connectors 2 have be joined, linking two separate pluralities of wires comprising aluminium 1. In this embodiment, the two connectors 2 are welded to one another using tungsten inert gas welding in a similar fashion as the manner in which each of the pluralities of aluminium comprising wires 1 were welded to their respective connectors 2. The solidified weld pool 5, comprising material from both the connectors 2, both the pluralities of wires comprising aluminium and, in some embodiments, a filler material 4, is depicted at where the two connectors 2 have been joined.

Claims

1. A method for welding wires comprising aluminium, the method comprising the steps of, placing a plurality of wires comprising aluminium proximal to a connector, heating said plurality of wires comprising aluminium and said connector to form at least one weld pool, and allowing said weld pool to cool and form a solidified weld pool such that said plurality of wires is welded to said connector.

2. The method of claim 1, further comprising the step of inserting said plurality of wires into said connector.

3. The method of claim 2, further comprising the step of inserting said plurality of wires into said connector such that said plurality of wires pass through a first aperture in said connector and protrude from a second aperture in said connector.

4. The method any preceding claim, wherein said connector comprises aluminium.

5. The method of any preceding claim, further comprising a step wherein a filler material is heated to provide additional material to said weld pool as part of the welding process.

6. The method of claim 3, wherein the filler material comprises aluminium.

7. The method of any one preceding claim, further comprising the step of undertaking the welding process at an aperture in the connector.

8. The method of claim 7, wherein at the termination of the welding process, said aperture in the connector is closed by said solidified weld pool.

9. The method of any one preceding claim, further comprising a step of insulating said plurality of wires comprising aluminium.

10. The method of any one preceding claim, wherein said connector and said plurality of wires comprising aluminium heated to form said weld pool have the same elemental composition as one another.

11. The method of any one of claims 1 to 9, wherein said connector and said plurality of wires comprising aluminium heated to form said weld pool have differing elemental compositions.

12. The method of any one preceding claim, wherein the welding process only results in localised heating of said plurality of wires comprising aluminium and said connector.

13. The method of any one preceding claim, further comprising the step of welding the plurality of wires comprising aluminium joined to said connector to at least one further plurality of wires comprising aluminium joined to at least one further connector.

14. The method of any one preceding claim, further comprising the step of welding the plurality of wires comprising aluminium joined to said connector to at least one further component.

15. The method of any one preceding claim, further comprising the step of using tungsten inert gas welding.

16. The method of claim 15, further comprising the step of striking an arc between 60 and 100 Amps during the tungsten inert gas welding process.

17. The method of claim 15 or claim 16, further comprising the step of an arc maintenance current of between 20 and 60 Amps during the tungsten inert gas welding process.

18. A method for welding wires comprising aluminium, substantially as hereinbefore described with reference to the accompanying drawings.

19. A connection between a plurality of wires comprising aluminium and a connector, the connection obtained by the method of any one preceding claim.